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Positron Distribution in the Inner Galactic Ridge

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OSSE was used to measure the longitude and latitude distribution of positron annihilation in the inner galactic ridge using differential measurements relative to intensities at latitudes of plus or minus 10 degrees. An improved understanding of the 50 keV to 10 MeV continua has recently permitted accurate determinations of the positronium continuum flux intensities this provides an - 5 times greater signal than was available in previous analyses which used only the 511 keV annihilation line. Within the statistical precision of the measurements, the line and positronium continuum components show indistinguishable distributions in both latitude and longitude. A differential measurement of their latitude distributions near the center indicates a narrow Gaussian ridge of -4.4 degrees FWHM. The longitude distribution of the ridge intensity differs from other known galactic ridge radiation distributions in that it shows a narrowly peaked maximum around the center. It can be characterized by an -12 degrees FWHM Gaussian central bulge plus a broad disk-like component. The only physical model based on plausibly associated galactic ridge distributions which can fit the observations well in longitude is the predicted galactic nova spheroid distribution, but scaled down by -23 from the latitude-integrated model bulge longitude width. The best fit has no additional discrete source or broad-disk components, although small contributions are permitted by the data. Novae are thought to be progenitors of Type I supernovae, probable sources of positrons in the galaxy, so this correlation suggests that Type I supernovae are the primary source of the positrons producing the observed galactic ridge annihilation radiation.

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  • Nuclear Physics and Elementary Particle Physics
  • Astrophysics

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